The invention is in the field of fusing and fusing apparatus for print media, particularly for fusing toner to print media and other variations.
Fusers are commonly implemented in electrographic print systems to fix toner, for example, to a print media such as a sheet of paper or plastic. Fuser temperature may be maintained by a feedback control loop that senses fuser roller surface temperature and turns heater lamps on and off in a pulse-width-modulated duty cycle to maintain roller temperature at a setpoint. At the beginning of a run, if the system has been in standby mode, fuser roller temperature is at, or very near, the desired setpoint. During the run, fuser roller temperature will undergo a transient decline, reaching a minimum and then begin to recover, eventually coming back up to the setpoint. During the transient, fuser roller temperature can fall to a level where fusing quality is compromised with reduced adhesion of the toner and increased crack-width in the fused toner. The amount of this transient “droop” depends on the heat capacity of the receiver, which in turn depends on the specific heat and mass of the receiver sheet.
Heavy coated papers represent a worst case due to greater mass and specific heat. One control scheme uses proportional-integral control with added feed-forward compensation to try to anticipate the transient droop and compensate by adding additional heat. The feed-forward is open loop since there is no sensor to measure heat removed by the receiver. An improved apparatus and control system is desired.